1. Field of the Invention
This invention relates to ducts used in the heating, ventilating, exhaust and/or air conditioning fields.
2. Description of Related Art
Ducts having circular, rectangular, or other cross sectional shape are used to transport heated or cooled air or other gasses from one place to another. A typical example is heated or cooled air from an air conditioner or furnace is transported to individual locations by a duct. These types of ducts are formed from sheet metal. The sheet metal is formed into a particular shape by taking ends of the sheet metal and interlocking them.
In circular duct work it is most common to have a self locking type of seam on the duct work that is put together by an installer. Typical examples of self locking mechanisms are reeves locks and button locks.
Previously, liquid (mastic) sealant was used for sealing rectangular duct work. Rectangular duct work is typically sold made to order. Manufacturers of rectangular ducts will manufacture the duct work to the specification of the installer. Therefore when supplying sealed rectangular ductwork it is already constructed prior to being shipped and the sealant is never exposed.
Circular duct work with reeves locks or button locks is typically shipped in bundles. An installer will then remove individual pieces from the bundle and then snap the seam of the duct together via the interlocking mechanism to create a circular duct. 5′ pieces are shipped with 1 piece locked with 4 pieces around it for a total of 5. 2′ pieces are shipped with 1 piece locked with 9 pieces around it for a total of 10 pieces. On some small sizes, all of the pieces can be locked.
However, these types of self locking mechanisms leak and cause inefficiency. This is problematic because of the cost of energy. A liquid sealant would not work with circular duct work having a self locking mechanism because the machines that manufacture the circular ductwork are not compatible with liquid sealant. The machines that manufacture circular ducts cannot use a liquid sealant because the liquid sealant will tend to flow or string outside of the applied area and onto the forming rolls. Once on the forming rolls, the machinery will not function properly. Because circular duct is shipped in bundles, parts of the duct where the liquid sealant is applied contact other parts of the duct. This causes the liquid sealant to adhere to the interior and/or exterior of the duct. The excess liquid sealant serves as dirt collection points for ducts in service and extra cleaning requirements for the exterior of exposed duct systems. No installer would buy circular duct work with a liquid sealant because the mess created by the liquid sealant would require additional cleaning. Additionally, when circular duct work is installed it may have to be cut by the installer. The cutting is done with the self locking mechanism disengaged. It sometimes becomes necessary for the installer to engage the self locking mechanism and then to disengage it. This is not possible with the liquid sealant that has been used in square duct work. If the liquid sealant is used with circular duct having a self locking mechanism and the self locking mechanism is disengaged, the integrity of the sealant would be compromised, thus causing failure to seal when re-engaged. Additionally, the sealant will be all over the inside and outside of the duct which will contaminate the air flow and can also collect dust on both the inside and outside of the duct. The collection of dust inside the duct can lead to mold growth, potentially creating indoor air quality hazards. The excess liquid sealant on the outside of the duct creates difficulty in painting the duct or resealing the duct as it could react with paint or sealant. The liquid sealant also off gasses VOCs into the air. Therefore, the liquid sealant is not used with circular duct work and there is no known circular duct work that is sold with sealant already applied.
Currently if a self locking circular sealed system is required, the installer assembles the ductwork and then has to use additional materials, such as tape or sealant and labor to have a sealed system.
There is a need for a sealed self locking circular system that does not require the installer to seal or tape the ductwork in order to reduce energy consumption and create efficiency.